Practical CoreBluetooth

An overview over the CoreBluetooth framework including many practical tips that can help developers.

Transcript

1. Practical CoreBluetooth Yoav Schwartz @Yoav_Schwartz NSCocoaHeads Copenhagen
2. • Introduction to BLE • Introduction to CoreBluetooth • Practical tips for CoreBluetooth development
3. What is BLE anyways? • Low power - can last months or even years on a single battery • Standard - Bluetooth 4.0 • Low cost - small, cheap and simple
4. Why BLE? • Heart rate monitor • Sensors • iBeacons(Proximity) • Internet of things
7. • Introduction to BLE • Introduction to CoreBluetooth • Practical tips for CoreBluetooth development
8. • Introduced iOS 5 • Wraps all of the BLE protocol into familiar iOS patterns CoreBluetooth?
9. CBCentralManager • Discovering and managing peripheral connections • Tip #1 - A manager cannot be used at all until the delegate receives a didUpdateState to .PoweredOn • manager = CBCentralManager(delegate:self, queue:nil, options: nil) • func centralManagerDidUpdateState(central: CBCentralManager!)
10. Scanning for devices • Discovering and managing peripherals • Tip #2 - Keep strong references to discovered peripherals, otherwise the system will throw them away • manager.scanForPeripheralsWithServices([CBUUID], options: nil) • manager.stopScan() • func centralManager(central: CBCentralManager!, didDiscoverPeripheral peripheral: CBPeripheral!, advertisementData: [NSObject : AnyObject]!, RSSI: NSNumber!)
11. Connecting to a peripheral • Tip #3 - Even though the protocol defines a timeout to the connection, apple choose to ignore it and continues indefinitely • Tip #4 - If you don’t keep a strong reference to the peripheral, the OS will automatically assume your’e not interested and drop the connection • manager.connectPeripheral(peri, options: nil) • manager.cancelPeripheralConnection(peripheral) - called both to cancel and disconnect • func centralManager(central: CBCentralManager!, didConnectPeripheral peripheral: CBPeripheral!) • func centralManager(central: CBCentralManager!, didDisconnectPeripheral peripheral: CBPeripheral!, error: NSError!)
12. Make the peripheral useful • Discovering the services offered • Tip #5 - This delegate is called on the same thread as set on the central manager • peripheral.discoverServices([CBUUID]) • func peripheral(peripheral: CBPeripheral!, didDiscoverServices error: NSError!) • peripheral.services
13. Useful, but we can do better • Discovering and reading the characteristics • Tip #6 - Unlike android, apple don’t distinguish between a read and a notification, Both call the didUpdateValueForCharacteritic. • peripheral.discoverCharacteristics(nil, forService: (service as CBService)) • func peripheral(peripheral: CBPeripheral!, didDiscoverCharacteristicsForService service: CBService!, error: NSError!) • peripheral.readValueForCharacteristic(characteristic) • peripheral.setNotifyValue(true, forCharacteristic: characteristic) • func peripheral(peripheral: CBPeripheral!, didUpdateValueForCharacteristic characteristic: CBCharacteristic!, error: NSError!)
14. Finally, writing something • Writing values to characteristics • peripheral.writeValue(data: NSData!, forCharacteristic: CBCharacteristic!, type: CBCharacteristicWriteType) • characteristic.properties - OptionSet type • characteristic.isNotifying • func peripheral(peripheral: CBPeripheral!, didWriteValueForCharacteristic characteristic: CBCharacteristic!, error: NSError!)
15. • Introduction to BLE • Introduction to CoreBluetooth • Practical tips for CoreBluetooth development
16. Subclassing CBPeripheral??? If only it was only that simple • Every operation will always return the basic CBPeripheral held magically somewhere in the CoreBluetooth stack • Composition to the rescue! • Object that is initialised with a CBPeripheral • Used to interact with the peripheral, keep a reference to it and act as it’s delegate
17. Connecting to the peripheral and the CBPeripheralDelegate • KVO to the rescue! • Instead of the didConnect and didDisconnect we observe the peripheral’s state property • We use the object we used in the previous slide as our CBPeripheralDelegate and give it the connection responsibility • Warning! - Since CBPeripheral doesn’t inherit from NSObject, KVO compliance is not guaranteed, however, it works, as this is standard behaviour
18. Determine proximity Deciding is in range • In the object in charge of the peripheral, keep a stack of the time/RSSI of the advertisements • Use the stack to determine proximity. The bigger the RSSI, the closer the device is. • In range is a bit more complicated, I use an average of the RSSI’s weighted by how long ago we got them (Sort of low pass filter) • Many possible implementations, very similar to determining WIFI strength for example • Gotcha! - Connected peripherals do not advertise, you have to call readRSSI manually to get a reading
19. Now what? • Apple’s CoreBluetooth Programming Guide • WWDC 2013 session on CoreBluetooth • WWDC 2012 session on CoreBluetooth • Altconf 2015 session on CoreBluetooth
20. Bonus • The iOS device can also be a peripheral itself! This is however too much to cover in a single talk • Even if you have no idea how to get/program a bluetooth chip, you can be a “firmware developer”. Implement any mock device using a second iOS device.
21. Yoav Schwartz @Yoav_Schwartz NSCocoaHeads Copenhagen